1. Field of the Invention
The present invention relates to a propylene-based polymer and a production method therefor, a propylene-based polymer composition and a molded body made thereof, in detail, the present invention relates to a method for producing polypropylene stably in high productivity, in particular, a propylene-based polymer having reduced amount of fine or lump, high bulk density and good fluidity, by using a specific gas-phase process in combination with a specific solid catalyst component, and a production method for a propylene-based block copolymer having reduced gel and excellent appearance characteristics, a propylene-based polymer produced thereby, a propylene-based polymer composition made thereof and a molded body made thereof.
2. Description of the Prior Art
Polypropylene is used for various applications because it has good physical properties such as rigidity and heat resistance, and can be produced in relatively low cost.
On the other hand, a production process of polypropylene has been technically improved for simplification of the production steps, reduction of production cost and enhancement of productivity. When industrial production of polypropylene had just begun, catalyst performance was low, and the steps for removing a catalyst residue and an atactic polymer from the obtained polypropylene was necessary, and such a process using a solvent as a slurry was dominant. By the following significant progress of catalyst performance, nowadays, a gas-phase process is dominant. Among the various gas-phase processes, a method for removing the heat of polymerization by utilizing the heat of vaporization of liquefied propylene is superior in heat removing capability with small facilities (refer to Patent Document 3 and the like).
As a gas-phase olefin polymerization reactor with the heat removal system by utilizing the heat of vaporization of liquefied propylene, there is known a horizontal reactor equipped with an agitator, which rotates around a horizontal axis thereof.
In general, catalyst particles gradually grow to polymer particles by a polymerization reaction. When polymerization is carried out in the horizontal reactor, these particles are gradually growing and moving along the shaft direction of the reactor by two forces of polypropylene generation by polymerization and mechanical agitation. Therefore, particles having the same growth degree, that is, having the same residence time, align with the residence time, from the upstream toward the downstream of the reactor. Therefore, in the horizontal reactor, the flow pattern is a piston-flow-type, making residence time distribution narrow to the same degree as in the case with several continuous stirring tank reactors in series. This is the excellent feature not observed in other types of polymerization reactors, and is economically advantageous in achieving the same mixing degree of solid particles easily with a single reactor as with 2, 3 or more reactors.
For polypropylene production, a method with the heat removal system for polymerization by utilizing the heat of vaporization of liquefied propylene, and with a horizontal reactor equipped with an agitator, which rotates around a horizontal axis thereof, has excellent characteristics as described above.
In this way, a gas-phase process utilizing the heat of vaporization of liquefied propylene has excellent characteristics, however, it has a problem to be solved such as modification for a highly active catalyst, which has been developed by progress of catalyst technology in recent years, improvement of power characteristics associated with it, and reduction of the amount of fines, which are easily blown up and fixed on to a pipeline. For example, vaporized gas passes through a gas exhaust line located at the upper part tank wall of a reactor, and is condensed by a condenser and used again as liquid coolant for heat removal. In the process using the heat of vaporization of liquefied propylene, a large amount of vaporized gas increases gas flow rate in a gas exhaust line system, which inevitably makes fines of polymer particles or the like accompanied with the vaporized gas (entrainment phenomenon), and causes adhering to the inside of a pipe or a filter of the gas exhaust line system, or clogging thereof. In the worst case, the process should be stopped for cleaning. Therefore, such a method has been proposed that a separation chamber is installed where un-reacted gas and cooled vapor exhausted from the upper part of the horizontal reactor pass through and where a liquid coolant is sprayed to reduce the amount of fines, or the like (for example, refer to Patent Document 3 or the like).
However, in the case of the high production pace, the amount of vaporized gas increases, in the worst case, such a problem appears that fines cannot be separated unless the diameter of the separation chamber is quite similar to that of the reactor, or additional facilities are required further.
In addition, in gas-phase polymerization achieving high polymerization activity, destruction of solid catalyst components during polymerization raises such problems as deterioration of the shape, generation of fines and deterioration of powder characteristics.
Furthermore, in order to achieve uniform residence time of the polymer particles in the tank, there are known various technologies and methods such as an agitating method of a horizontal-mono-axial type with many rectangular-shape flat paddles on the horizontal rotating shaft (for example, refer to Patent Document 4 or the like); an agitator able to continuously operate with one or more rotating baffles fixed on the rotating shaft (for example, refer to Patent Document 5 or the like); or an agitator having tanks partitioned by baffles fixed vertically to the rotating shaft on the inner wall of the tank (for example, refer to Patent Document 5 or the like); and the like. By these known technologies, uniform residence time in the horizontally agitated bed reactor system, and reduction of short-pass particles and the amount of fines in the agitator have been pursued.
Therefore, it has been desired to develop a technology to reduce the amount of fines, which could cause troubles, in “a gas-phase process where the heat of reaction is removed mainly by using the heat of vaporization of liquefied propylene”, having high production capability with compact facilities and advantage that high catalyst activity can be achieved.
In addition, in the case of producing polypropylene having high MFR value recently desired, there is a problem to be solved in view of productivity. In the case of utilizing the heat of vaporization of liquefied propylene, it is a general method to exhaust a gas from a polymerization reactor, to be liquefied by cooling with a heat exchanger, and to return again into the polymerization reactor. Because the temperature at which the gas is liquefied (due point) depends on the pressure and the gas composition, by adding such a gas component having low due point as hydrogen or ethylene into propylene, due point decreases in comparison with that of pure propylene. Cooling capability of the heat exchanger is determined by a facility, therefore, when the same facility is used, lower due point of the gas component lowers the capability to liquefy the gas, that is, lowers the heat removal capability. On the other hand, for polypropylene production, it is general to use hydrogen, which can induce a chain transfer reaction, as an agent to control the molecular weight. In order to produce polypropylene having higher MFR value, that is, lower molecular weight, hydrogen must be used in higher concentration. Therefore, in the gas-phase process utilizing the heat of vaporization of liquefied propylene, when polypropylene having high MFR value is produced, a problem of reduced productivity appears by the heat removal limitation.
There have been several proposals on methods for solving these problems by catalyst improvement. First, for the problem of fines, for example, a method for spraying a molten mixture of a magnesium compound and an alcohol to obtain a mixture and then supporting a halogen-containing component on a solid catalyst (for example, refer to Patent Document 6); and also a method characterized by using a specific silane compound having an Si—O—C bond, have been proposed. In addition, a method for prepolymerizing a catalyst is also known, and a method for using a specific catalyst component prepolymerized with ethylene has been proposed (for example, refer to Patent Document 7). Furthermore, a method for conducting prepolymerization under the higher pressure than that in a gas-phase polymerization reactor was also proposed (for example, refer to Patent Document 8).
On the other hand, in order to produce polypropylene having high MFR value, it is effective to employ a catalyst system having high hydrogen response, and for example, there have been proposed a method for using an organoaluminum component in combination with an aluminoxane as co-catalysts (for example, refer to Patent Document 9); a method for using an organoaluminum component in combination with an organozinc component as co-catalysts (for example, refer to Patent Document 10); a method for supporting a halogen-containing component on a solid catalyst (for example, refer to Patent Document 11); a method for using an organosilicon compound having an amino group (for example, refer to Patent Documents 12, 13 and 14); a method for using a specific organosilicon compound having both a branched or aliphatic cyclic hydrocarbon group and an amino group (for example, refer to Patent Documents 15 and 16) and the like.
In addition, in view of enhancing productivity, a method for using a highly active catalyst is considered. The present applicants have found that a highly stereospecific and highly active catalyst can be obtained by using a specific vinylsilane compound as a polymerization catalyst for propylene, and have filed patent application (refer to Patent Document 1 and 2 and the like). This method highly improves stereospecificity and activity, however, did not improve the productivity of a propylene-based polymer having high MFR value, especially in a slurry polymerization process or the like.
Therefore, as far as the present inventors know, there has not yet been proposed a method with sufficient performance in view of the productivity of polypropylene having high MFR value, and furthermore, it has been desired to develop an improved technology reducing the amount of fines, and having good powder characteristics and high polymerization activity at the same time. In particular, in a gas-phase process having the heat removal system for polymerization utilizing the heat of vaporization of liquefied propylene, which is advantageous in productivity, it has been desired to apply the most effective catalyst system.    Patent Document 1: JP-A-59-230010    Patent Document 2: JP-A-3-234707    Patent Document 3: JP-A-63-199203    Patent Document 4: JP-A-63-23721    Patent Document 5: JP-A-62-227431    Patent Document 6: JP-A-8-127615    Patent Document 7: JP-A-5-117317    Patent Document 8: JP-A-6-122724    Patent Document 9: JP-A-7-25927    Patent Document 10: JP-A-8-67710    Patent Document 11: JP-A-2000-7725    Patent Document 12: JP-A-8-3215    Patent Document 13: JP-A-2004-315742    Patent Document 14: JP-A-2005-48045    Patent Document 15: JP-A-8-100019    Patent Document 16: JP-A-8-157519